1. Field of the Invention:
This invention relates to the use of difference-in-time-of-arrival apparatus for direction finders and signal sorters, as well as for reducing the detrimental effects of multipath transmission in television receivers, and, more particularly, to an improved auto-correlator for.such difference-in-time-of-arrival apparatus.
2. Description of the Prior Art
There are several known types of direction finders that incorporate a radio-wave-signal receiver. Such direction finders are useful in determining the azimuth (and/or elevation) direction of a particular radio-wave-signal transmitter. The most common type of direction finder, which requires that the frequency of the the particular radio-wave-signal transmitter be known, comprises a radio-wave-signal receiver incorporating a fixed phased array or movable directional antenna tuned to the known given frequency. Another known type of direction finder, with which the present invention is concerned, does not require that the frequency of the the particular radio-wave-signal transmitter be known. Instead, this other known type of direction finder, which comprises two similar fixed antennas that are spaced a given fixed distance apart, determines the direction of any of all the radio-wave signals then being received by the two fixed antennas in accordance with the difference in time of arrival of such signals at each of the two fixed antennas. Specifically, when a variable time delay means coupled to one of the two antennas is adjusted to provide a certain time delay equal to the difference in time of arrival of a given signal arriving from a given direction with respect to a line connecting the two antennas, only the delayed given signal received by the one antenna will be correlated with the given signal received by the other antenna. An auto-correlator is used to detect the correlated given signal arriving from the given direction.
However, each of the two antennas is capable of receiving all frequencies within the same broad frequency band defined by the similar structure of each of the two antennas. Therefore, each antenna normally receives radio-wave signal power occurring at many different frequencies within this frequency band and arriving from many different directions. At a time-delay value corresponding to the direction of the given signal, the value of the total power output from the auto-correlator will include (1) a desired correlated.component proportional substantially to all the radio-wave frequency power arriving at the two antennas from the given direction, and (2) an undesired uncorrelated component resulting from some unknown fraction of the sum of the radio-wave frequency power arriving at the two antennas from all other directions from that of the given direction.
The present invention is primarily directed to the structure of an improved auto-correlation means that is capable of maximizing, or at least increasing, the radio between the aforesaid desired correlated-component power and the undesired uncorrelated-component power, which together compose the total power output value thereof, thereby increasing the selectivity and accuracy of a difference-in-time-of-arrival direction finder which incorporates such improved auto-correlation means. In addition to its use as a direction finder, similar difference-in-time-of-arrival equipment is useful as a signal sorter.